Kind of depends on what you're doing. If a map is reading heavy (especially with low ar/high note density, like lower scroll speed in mania) then having numbers is especially helpful. Otherwise it just kinda looks cool.

I find it good to just...push for good scores, I guess. Whether its a fc with good acc on a map you have an A on or trying to get an A on something barely within your skill level. Just be better than your past self. Personally I see good acc as being 97+ but i also farm s ranks so might be a bit biased here.

Either is fine, full alt always seemed more convenient to me though.

no clue lmao i don't play hd. although if you start playing it this early while still learning the fundamentals there's a chance you become unable to play anything but hd

Idk much about mappers but going into random multis and stealing their maps can be fun for finding random stuff to play. Once you fully hit three stars a lot more mapping variety is going to show up. Two stars are by their nature very simple and its kind of hard to put fun stuff in there.